1. Field of Invention
This invention relates to visual displays, which are generated by relying on the observer's “persistence of vision” or the “after image effect” of human vision.
2. Description of Prior Art
The “after image effect” or the “persistence of vision” of the human eye is well known as a viable means of delivering readable displays to the brain. Devices, which have been used to produce such displays, will display small portions of an image at different times and locations, relying on the human brain to retain the momentary images and combine them into a whole picture. Such displays are visibly pleasing and seem to appear and hang in mid-air. Motion is an integral part of the production of an “after image” display. The device, which produces the display, may be moved through space or the observer may be moved. Either way, the phenomenon is effective and visual displays become perceptible by the brain.
Bell U.S. Pat. No. 4,470,044 teaches that saccadic eye movements can produce visual displays without moving the display device, but this is only effective when viewed at a distance, since minute eye movements cannot scan the required space when viewed in close proximity.
The “after image effect” relies on partial images delivered to the brain in rapid succession.
The human brain must retain the partial images long enough to construct a meaningful image out of them. The faster the partial images are presented to the eye/brain, the faster the brain can make sense of the image and perceive a visual display.
This phenomenon has been illustrated in various displays at the Exploratorium in San Francisco, Calif. and at other Exploratorium sites. The following internet sites are instructive on persistence of vision and the “after image effect”.
http://www.exploratorium.edu/exhibit_services/exhibits/p/persistenceofvision.html
http://www.exploratorium.edu/exhibit_services/exhibits/t/tripleeyelightstick.html
Highly complicated and costly apparatus has been employed as in Belcher et al. U.S. Pat. No. 5,302,965 and in Sokol U.S. Pat. No. 4,689,604 to deliver precisely timed displays in order to attempt a stable display. Not only are the apparatus costly, but if they are not precisely synchronized with the motion of the display device, the display will not be stable and pleasing.
Some have attempted to synchronize the display to the motion of the device using an accelerometer, such as in Tokimoto et al. U.S. Pat. No. 5,406,300. This technique has proved to be too complicated and expensive for a low cost device.
Jim Phillips and Rich Ottosen demonstrated the after image effect with their Whirlessgig but it was hard to see the message displayed. They also suggest using an accelerometer to detect the swing of the device but this would make it prohibitively expensive as well as requiring periodic calibration and adjustment of the accelerometer. Their work is documented on the internet at http://www.brouhaha.com/˜eric/pic/whirlessgig.html.
Users of prior art displays have been unable to see the display when it is directed away from them while demonstrating the device to others. This makes use of the display unreliable, since the user is never sure if the correct display is visible, or if this swing is producing a pleasing display.
Ohta et al. U.S. Pat. No. 5,444,456 attempts to remedy this lack of positive feedback problem, by using light guides to direct the display in two directions at once. This allows both the user and the viewer to see a display, but the user will always see a mirror image of what is being displayed for the viewer. Only symmetrical objects can be displayed correctly on both sides of the device. This limitation of only being able to display symmetrical objects is manifest in “The Picture Stick” by Scott Edwards. Published in Electronics Now, October 1994 v65 n10 p35. This device also lacked any method of synchronizing the display with the motion of the picture stick. The result is unstable, unpredictable displays. Prior art that is swung in a rotational manner has a similar problem of reversal since the display is visible through 360 degrees of rotation, most of which is displayed backwards.
If the kinetic motion of the swing or rotational device is not properly sensed, portions of the display may be reversed, bunched, shifted, jittery, too narrow, too wide, or not centered, rendering the display unusable.
Prior art has been heavy, cumbersome, and limited to a vertical row of light emitting elements, which limits the size and shape of the device.
Prior art has not be able to display large displays, or communicate large phrases, since they are limited to what can be displayed in one swing.
Determining what is to be displayed by prior art is complicated and time consuming. Data selection has been accomplished with complicated push button selection schemes without user feedback to verify correct programming. Users of the devices quickly become frustrated with the complicated device and lose interest in using it. Some devices have provided means for users to enter user defined display data. These means all suffer from highly complicated methods and means, which confuse and discourage users.
Sensors for synchronizing the display with the motion of the display device have been mounted at either end of the light-emitting array in prior art. This tends to distort the display since it was not sensed within the space of the visual image.
Prior art has only a single display mode, or method of display which severely limits the uses and applications of the device.
Prior art has stored display data as bit maps, which severely limits the number of characters that can be displayed and requires large amounts of expensive memory.